Commercially important sources of pyridine bases are tar and saturated liquor obtained by the carbonization of coal. However, the stringent specifications laid down for these products in pharmaceuticals and agricultural applications cannot be met from natural sources, namely from coal carbonization byproducts. Amongst the various synthetic routes, the reaction between acetaldehyde and ammonia is the most common one known in the prior art for making pyridine bases.
Acids have been used as catalysts or co-catalysts in a number of reactions. U.S. Pat. No. 2,186,392 reveals that ethanolamines may be produced from ammonia or a primary amine and ethylene oxide and a salt of a weak acid, such as ammonium carbonate, in the presence of an aliphatic radical which is positive with respect to hydrogen. German Patent 844,449 (CA 48:1429c) informs tertiary amines with hydroxyalkyl radicals may be made from ammonia, primary or secondary amines and an alkylene oxide at a temperature of from 30° C. to 60° C., with improved yields being possible if water or a weak acid is also present. British Patent No. 497,093, (CA 36:4131-8) indicates that monoalkanolamines may be made from olefin oxides and ammonia in the presence of water and an acid.
The reaction of acetaldehyde or certain other low molecular weight aldehydes and ammonia either in the absence or presence of methanol and/or formaldehyde to yield pyridine and alkyl derivatives thereof has heretofore been carried out in the presence of amorphous silica-alumina composites containing various promoters. The yields of desired products using the latter catalysts have been poor. Alkylpyridines have also been synthesized, as reported in Advances in Catalysis, Volume 18, page 344 (1968) Academic Press, Inc., New York, N.Y., by passing gaseous acetaldehyde and ammonia over crystalline aluminosilicates, NaX and H-mordenite. While initial conversion utilizing these materials as catalysts was high, catalyst deactivation by coking was rapid, providing a commercially unattractive system, characterized by poor catalytic stability.
U.S. Pat. No. 4,220,783 provides a method for synthesizing pyridine or alkylpyridines by reacting ammonia and a carbonyl reactant which is an aldehyde containing 2 to 4 carbon atoms, a ketone containing 3 to 5 carbon atoms or mixtures of said aldehydes and/or ketones under effective conditions in the presence of a catalyst comprising a crystalline aluminosilicate zeolite having a silica to alumina ratio of at least about 12 and a constraint index within the approximate range of 1 to 12 and recovering from the resulting reaction mixture, a product containing at least one compound of pyridine or an alkylpyridine. Addition of methanol and/or formaldehyde to the feed improves selectivity to unsubstituted pyridine. The yields of desired products have been poor. Manufacture of pyridine bases by employing the catalyst causes environmental pollution because these routes use toxic ThO2 and CdO. The catalyst preparation involves tedious method for the preparation of silica alumina gel.